Spectral-kinetic characteristics of the undoped and Eu3+-doped alkali gadolinium phosphates of the type of MGdP4O12 (M = Li, Na) have been studied within the 4.2–300 K temperature range using time-resolved luminescence spectroscopy techniques. The photon cascade luminescence of Gd3+ ions in the undoped LiGdP4O12 phosphate has been observed. In the case of the Eu3+-doped MGdP4O12 phosphates, no quantum cutting process takes place due to the spectral overlap of the charge transfer band of Eu3+ with the bands arising from the 6GJ levels of Gd3+. The processes of energy migration along the Gd3+ sublattice and the Gd3+ → Eu3+ energy transfer have been studied. The phonon-assisted population of the Gd3+ 6P5/2,3/2 excited levels is suggested to be responsible for the increase in the probability of the energy migration along the Gd3+ sublattice via the 6PJ states with the subsequent energy transfer to the 5IJ levels of an Eu3+ ion.